Air-conditioning apparatus

ABSTRACT

An air-conditioning apparatus includes a first branch unit, a fourth flow control device arranged in each of a plurality of pipes split from a first connection pipe side and connected to each indoor-side heat exchanger, and a solenoid valve arranged in each of pipes split from a pipe connecting each fourth flow control device and each indoor-side heat exchanger. An opening degree of the fourth flow control device is controlled based on a state of refrigerant to be caused to flow into the fourth flow control device.

TECHNICAL FIELD

The present invention relates to an air-conditioning apparatus to be used as, for example, a multi-air-conditioning apparatus for a building, including a refrigerant circuit and structure capable of efficiently supplying one or both of heating energy and cooling energy generated by a heat source unit to a plurality of loads.

BACKGROUND ART

Hitherto, air-conditioning apparatus such as a multi-air-conditioning apparatus for a building are configured to execute a cooling operation or a heating operation by circulating refrigerant between, for example, an outdoor unit serving as a heat source unit arranged outdoors and an indoor unit arranged indoors. Specifically, an air-conditioned space is cooled or heated with air that is cooled by refrigerant taking away heat or air that is heated by refrigerant rejecting heat. As the refrigerant to be used for such an air-conditioning apparatus, for example, a hydrofluorocarbon (HFC)-based refrigerant is often used. In addition, it is also suggested to use a natural refrigerant such as carbon dioxide (CO₂).

As such an air-conditioning apparatus, there is given an air-conditioning apparatus capable of performing cooling and heating operations by connecting a heat source unit and a plurality of indoor units to supply refrigerant from the heat source unit to each of the plurality of indoor units (see, for example, Patent Literature 1). The air-conditioning apparatus as disclosed in Patent Literature 1 includes a first branch unit (10) including three-way switching valves (8) for switchably connecting first connection pipes (6 b, 6 c, and 6 d) and a first connection pipe (6) or a second connection pipe (7), and a second branch unit (11) for connecting second connection pipes (7 b, 7 c, and 7 d) on an indoor unit side and the second connection pipe (7) through check valves (50 b, 50 c, 50 d, 52 b, 52 c, and 52 d).

In the air-conditioning apparatus as disclosed in Patent Literature 1, each of the three-way switching valves (8) in the first branch unit (10) switches refrigerant to be caused to flow into the indoor unit intended for the heating operation and refrigerant flowing in from the indoor unit that is performing the cooling operation. In addition, each check valve constructing the second branch unit (11) allows the refrigerant to unidirectionally flow in accordance with the switching of the refrigerant in the first branch unit (10). Therefore, when the indoor unit performs the cooing operation, one of connection ports (first port 8 a) of the three-way switching valve (8) is closed, whereas two of the connection ports (second port 8 b and third port 8 c) are opened. In addition, when the indoor unit performs the heating operation, one of the connection ports (second port 8 b) is closed, whereas two of the connection ports (first port 8 a and third port 8 c) are opened.

In addition, when the indoor unit performs the cooling operation, a pressure of the refrigerant is low in the first connection pipe (6) and high in the second connection pipe (7). Therefore, the pressure is high in a connection pipe on one connection port (first port 8 a) side of the three-way switching valve (8) and low in a connection pipe on another connection port (second port 8 b) side. Further, the pressure is low in a connection pipe on still another connection port (third port 8 c) side. In addition, during the cooling operation, the refrigerant is controlled in accordance with an outlet superheating amount of an indoor-side heat exchanger (5), and the refrigerant in a low-pressure gas state flows in the first connection pipes (6 b, 6 c, and 6 d) on the indoor unit side.

Further, when the indoor unit performs the heating operation, the pressure of the refrigerant is low in the first connection pipe (6) and high in the second connection pipe (7). Therefore, the pressure is high in the connection pipe on one connection port (first port 8 a) side of the three-way switching valve (8) and low in the connection pipe on another connection port (second port 8 b) side. Further, the pressure is high in the connection pipe on still another connection port (third port 8 c) side. In addition, during the heating operation, a flow rate of the refrigerant is controlled in accordance with an outlet subcooling amount of the indoor-side heat exchanger (5), and the refrigerant in a high-temperature and high-pressure gas state flows in the first connection pipes (6 b, 6 c, and 6 d) on the indoor unit side. The refrigerant in a high-temperature and high-pressure liquid state is present in the indoor-side heat exchanger (5) and in a connection pipe ranging from the indoor-side heat exchanger (5) to first flow control devices (9).

Therefore, when the operation of the connected indoor unit is switched from the heating operation to the cooling operation, the high-temperature and high-pressure gas refrigerant and the high-temperature and high-pressure liquid refrigerant that flow during the heating operation pass through the three-way switching valve (8) to flow into the first connection pipe (6), which is in a low-pressure state. When the operation of the connected indoor unit is switched from the heating operation to the cooing operation, refrigerant flow noise is generated in the three-way switching valve (8) depending on the balance between the high pressure and the low pressure of the refrigerant that passes through the three-way switching valve (8). In particular, the flow noise of the high-temperature and high-pressure liquid refrigerant is significant.

Thus, there is given an air-conditioning apparatus using solenoid valves (solenoid opening/closing valves) in place of the three-way switching valves (8) (see, for example, Patent Literature 2). In the air-conditioning apparatus as disclosed in Patent Literature 2, a second solenoid valve (8 b) is used for heating, whereas a first solenoid valve (8 a) and a third solenoid valve (8 c) with an orifice function are used for cooling. When the operation is switched to the cooling operation, the refrigerant is caused to flow into the first and third solenoid valves in a stepwise manner to reduce the flow noise of the high-temperature and high-pressure liquid refrigerant. In addition, in the air-conditioning apparatus as disclosed in Patent Literature 2, the refrigerant flow noise is reduced by reducing an opening diameter of the flow control device, pulse-controlling the flow control device, or reducing an opening diameter of the third solenoid valve.

In addition, there is also given another air-conditioning apparatus downsized by using solenoid valves (solenoid opening/closing valves) in place of the three-way switching valves (8) (see FIG. 6). In this air-conditioning apparatus, a second solenoid valve b is used for heating, whereas a first solenoid valve a, a third solenoid valve c, and an orifice d are used for cooling. In other words, in the air-conditioning apparatus as illustrated in FIG. 6, the refrigerant is caused to flow into the orifice d, the third solenoid valve c, and the first solenoid valve a in a stepwise manner to reduce the flow noise of the high-temperature and high-pressure liquid refrigerant when the operation is switched to the cooling operation. Note that, in FIG. 6, the same reference signs are assigned to components corresponding to those of the air-conditioning apparatus according to an embodiment of the present invention.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent No. 4350836 (Embodiment 1, FIG. 1, etc.)

Patent Literature 2: Japanese Unexamined Patent Application Publication No. Hei 09-042804 (FIG. 1, etc.)

SUMMARY OF INVENTION Technical Problem

According to the air-conditioning apparatus as disclosed in Patent Literature 2 and FIG. 6, one indoor unit requires three solenoid valves, thereby being necessary to arrange as many solenoid valves in the branch unit as the number of indoor units multiplied by three. Pressure equalization is required to reduce the refrigerant flow noise, but the control using solenoid valves cannot achieve fine flow control. Thus, regardless of the pressure state of the refrigerant that flows in from the connection pipe on the indoor unit side, it is necessary to equalize the pressure on the refrigerant over a given period of time, leading to failure to optimize a startup time period of the indoor unit as well as insufficient reduction of the refrigerant flow noise.

The present invention is to solve the problem as described above, and an object of the present invention is to provide an air-conditioning apparatus capable of enhancing comfort by reducing a startup time period of an indoor unit while maintaining silence in running.

Solution to Problem

According to one embodiment of the present invention, there is provided an air-conditioning apparatus, which is configured by connecting a heat source unit and a plurality of indoor units through a first connection pipe and a second connection pipe to supply refrigerant from the heat source unit to each of the plurality of indoor units to perform a cooling operation and/or a heating operation, the heat source unit including a compressor, a switching valve, and a heat-source-unit-side heat exchanger, each of the plurality of indoor units including an indoor-side heat exchanger and a first flow control device, the air-conditioning apparatus including: a first branch unit for switchably connecting one of a refrigerant inlet and a refrigerant outlet of the indoor-side heat exchanger of each of the plurality of indoor units to the first connection pipe or the second connection pipe; and a second branch unit connected on one side thereof to the second connection pipe and split on an other side thereof into a plurality of branches each connected to an other one of the refrigerant inlet and the refrigerant outlet of the indoor-side heat exchanger of each of the plurality of indoor units through the first flow control device, the first branch unit including: a branch-side flow control device provided to each of a plurality of pipes split from the first connection pipe and connected to the indoor-side heat exchanger of corresponding one of the plurality of indoor units; and a solenoid valve provided to each of pipes split from a pipe connecting the branch-side flow control device and the indoor-side heat exchanger of corresponding one of the plurality of indoor units, wherein an opening degree of the branch-side flow control device is controlled based on a state of the refrigerant to be caused to flow into the branch-side flow control device.

Advantageous Effects of Invention

According to the air-conditioning apparatus of the one embodiment of the present invention, it is possible to determine an appropriate opening degree of the branch-side flow control device based on the state of the refrigerant to be cased to flow into the branch-side flow control device, thereby being capable of reducing the refrigerant flow noise and the startup time period of the indoor unit as compared to the case of switching a plurality of solenoid valves in a stepwise manner over a given period of time. As a result, the comfort is enhanced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an overall configuration diagram focusing on a refrigerant system of an air-conditioning apparatus according to an embodiment of the present invention.

FIG. 2 illustrates an operation state of the air-conditioning apparatus during cooling and heating operations (cooling only operation) according to the embodiment of the present invention.

FIG. 3 illustrates an operation state of the air-conditioning apparatus during cooling and heating operations (heating only operation) according to the embodiment of the present invention.

FIG. 4 illustrates an operation state of the air-conditioning apparatus during cooling and heating operations (cooling main operation) according to the embodiment of the present invention.

FIG. 5 illustrates an operation state of the air-conditioning apparatus during cooling and heating operations (heating main operation) according to the embodiment of the present invention.

FIG. 6 is a circuit configuration diagram schematically illustrating an example configuration of a relay unit of a related-art air-conditioning apparatus.

FIG. 7 is a flowchart illustrating an example flow of processing for controlling an opening degree of a fourth flow control device 55 of the air-conditioning apparatus during a refrigerant noise suppression operation according to the embodiment of the present invention.

FIG. 8 is a flowchart illustrating an example flow of processing for determining whether the refrigerant noise suppression operation is necessary for the air-conditioning apparatus according to the embodiment of the present invention.

FIG. 9 is a flowchart illustrating an example flow of processing for determining whether the refrigerant noise suppression operation is necessary for the air-conditioning apparatus according to the embodiment of the present invention.

FIG. 10 is a flowchart illustrating an example flow of processing for determining whether the refrigerant noise suppression operation is necessary for the air-conditioning apparatus according to the embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Now, an embodiment of the present invention is described referring to the drawings. Note that, in the drawings referred to below including FIG. 1, the size relationship between components may be different from the reality in some cases. Further, in the drawings referred to below including FIG. 1, the same or corresponding parts are represented by the same reference signs, and the same applies hereinafter. Further, the forms of the constituent elements described herein are only examples and the present invention is not limited to the forms described.

FIG. 1 is an overall configuration diagram focusing on a refrigerant system of an air-conditioning apparatus 100 according to an embodiment of the present invention. In addition, FIGS. 2 to 5 illustrate an operation state of the air-conditioning apparatus 100 during cooling and heating operations. FIG. 2 is an operation state diagram for a cooling only operation. FIG. 3 is an operation state diagram for a heating only operation. FIG. 4 is an operation state diagram for a cooling main operation in which cooling operation capacity is larger than heating operation capacity in a cooling and heating simultaneous operation. FIG. 5 is an operation state diagram for a heating main operation in which heating operation capacity is larger than cooling operation capacity in the cooling and heating simultaneous operation. Note that, in this embodiment, the case of connecting three indoor units to one heat source unit is described, but the case of connecting two or more indoor units is the same.

As illustrated in FIG. 1, the air-conditioning apparatus 100 includes a heat source unit A, indoor units B, C, and D (hereinafter each simply referred to as “indoor unit” unless otherwise mentioned), and a relay unit E, which are connected to each other. The heat source unit A has a function to supply heating energy or cooling energy to the indoor units. As described later, the indoor units are connected to each other in parallel, and have the same configuration. Each indoor unit has a function to execute air-conditioning of an air-conditioned space such as an indoor space by heating energy or cooling energy supplied from the heat source unit A. The relay unit E is arranged between the heat source unit A and the indoor units, and has a function to switch the flow of refrigerant supplied from the heat source unit A in response to a request from the indoor units.

The heat source unit A includes a compressor 1 with variable capacity, a four-way switching valve 2 for switching a flow direction of the refrigerant in the heat source unit A, a heat-source-unit-side heat exchanger 3 that functions as an evaporator or condenser (radiator), an accumulator 4 that is connected to a suction side of the compressor 1 through the four-way switching valve 2, a heat-source-unit-side fan 20 that can change air-sending amount for sending air to the heat-source-unit-side heat exchanger 3, and a heat-source-unit-side switching valve 40 for limiting the flow direction of the refrigerant. Further, those components construct the heat source unit A. Note that, the four-way switching valve 2 corresponds to the “switching valve” of the present invention. Note that, the “switching valve” may include a combination of valves such as a two-way valve and a three-way valve, instead of the four-way switching valve.

The indoor unit includes an indoor-side heat exchanger 5 that functions as a condenser (radiator) or evaporator, and a first flow control device 9 that is controlled in accordance with an outlet-side superheating amount of the indoor-side heat exchanger 5 during cooling and is controlled in accordance with an outlet-side subcooling amount of the indoor-side heat exchanger 5 during heating. Further, those components construct the indoor unit.

The relay unit E includes, as built-in devices, a first branch unit 10, a second flow control device 13, a second branch unit 11, a gas-liquid separating device 12, heat exchange units (first heat exchange unit 19 and second heat exchange unit 16), and a third flow control device 15. Further, those components construct the relay unit E.

The four-way switching valve 2 in the heat source unit A and the relay unit E are connected by a thick first connection pipe 6.

The indoor-side heat exchanger 5 in the indoor unit and the relay unit E are connected by a first connection pipe 6 b, 6 c, or 6 d on the indoor unit side, which corresponds to the first connection pipe 6.

The heat-source-unit-side heat exchanger 3 in the heat source unit A and the relay unit E are connected by a second connection pipe 7 that is thinner than the first connection pipe 6.

The indoor-side heat exchanger 5 in the indoor unit and the relay unit E are connected through the first connection pipe 6, and are also connected by a second connection pipe 7 b, 7 c, or 7 d on the indoor unit side, which corresponds to the second connection pipe 7.

The first branch unit 10 has a function to switchably connect the first connection pipes 6 b, 6 c, and 6 d on the indoor unit side and the first connection pipe 6 side or the second connection pipe 7 side.

The first branch unit 10 includes fourth flow control devices (branch-side flow control devices) 55 that are connected to the respective first connection pipes 6 b, 6 c, and 6 d on the indoor unit side and to the first connection pipe 6, and solenoid valves 31 as valve devices that are connected to the respective first connection pipes 6 b, 6 c, and 6 d on the indoor unit side and to the second connection pipe 7 side.

The second branch unit 11 has a function to switch the connection between the second connection pipes 7 b, 7 c, and 7 d on the indoor unit side and the second connection pipe 7 in accordance with the flow of the refrigerant.

The second branch unit 11 includes first check valves 50 (first check valves 50 b, 50 c, and 50 d) described later, and second check valves 52 (second check valves 52 b, 52 c, and 52 d) described later.

The gas-liquid separating device 12 is arranged in the middle of the second connection pipe 7, and includes a gas-phase portion connected to the solenoid valves 31 of the first branch unit 10 and a liquid-phase portion connected to the second branch unit 11.

The second flow control device 13 is arranged between the gas-liquid separating device 12 and the second branch unit 11 on the second connection pipe 7 and includes, for example, an electric expansion valve that is openable and closable.

Note that, the second branch unit 11 and the first connection pipe 6 are connected by a first bypass pipe 14.

The third flow control device 15 is arranged in the middle of the first bypass pipe 14 and includes, for example, an electric expansion valve that is openable and closable.

The second heat exchange unit 16 is arranged on a downstream side of the third flow control device 15 on the first bypass pipe 14, and exchanges heat with a part on a downstream side of the second flow control device 13 on the second connection pipe 7.

The first heat exchange unit 19 is arranged on a downstream side of the second heat exchange unit 16 on the first bypass pipe 14, and exchanges heat with a part on an upstream side of the second flow control device 13 on the second connection pipe 7.

The first check valves 50 b, 50 c, and 50 d are arranged, respectively, in the middle of the second connection pipes 7 b, 7 c, and 7 d on the indoor unit side in the second branch unit 11, and allow the refrigerant to flow only from the second connection pipe 7 to the second connection pipes 7 b, 7 c, and 7 d on the indoor unit side.

Note that, a downstream part of the second check valves 52 b, 52 c, and 52 d of the second connection pipes 7 b, 7 c, and 7 d on the indoor unit side, and a pipe portion on the downstream side of the second flow control device 13 of the second connection pipe 7 and on an upstream side of the second heat exchange unit 16 are connected by a second bypass pipe 51. Further, a pipe in the second bypass pipe 51 that is connected to the second connection pipes 7 b, 7 c, and 7 d on the indoor unit side and a pipe in the second bypass pipe 51 that is connected to the second connection pipe 7 join together in the middle.

The second check valves 52 b, 52 c, and 52 d are arranged in an upstream part with respect to a part where the pipe in the middle of the second bypass pipe 51 that is connected to the second connection pipes 7 b, 7 c, and 7 d on the indoor unit side, and the pipe in the second bypass pipe 51 that is connected to the second connection pipe 7 join together, and allow the refrigerant to flow only from the second connection pipes 7 b, 7 c, and 7 d on the indoor unit side to the second connection pipe 7.

Note that, a first refrigerant passage is formed by a passage that leads from the second connection pipe 7 to the first flow control device 9 through the second connection pipes 7 b, 7 c, and 7 d on the indoor unit side including the first check valves 50 b, 50 c, and 50 d. A second refrigerant passage is formed by a passage that leads from the first flow control device 9 to the second connection pipe 7 through the second connection pipes 7 b, 7 c, and 7 d on the indoor unit side and the second bypass pipe 51 including the second check valves 52 b, 52 c, and 52 d.

A third check valve 32 is arranged in the middle of a pipe that connects the heat-source-unit-side heat exchanger 3 and the second connection pipe 7, and allows the refrigerant to flow only from the heat-source-unit-side heat exchanger 3 to the second connection pipe 7.

A fourth check valve 33 is arranged in the middle of a pipe that connects the four-way switching valve 2 in the heat source unit A and the first connection pipe 6, and allows the refrigerant to flow only from the first connection pipe 6 to the four-way switching valve 2.

A fifth check valve 34 is arranged in the middle of a pipe that connects the four-way switching valve 2 in the heat source unit A and the second connection pipe 7, and allows the refrigerant to flow only from the four-way switching valve 2 to the second connection pipe 7.

A sixth check valve 35 is arranged in the middle of a pipe that connects the heat-source-unit-side heat exchanger 3 and the first connection pipe 6, and allows the refrigerant to flow only from the first connection pipe 6 to the heat-source-unit-side heat exchanger 3.

The third check valve 32, the fourth check valve 33, the fifth check valve 34, and the sixth check valve 35 construct the heat-source-unit-side switching valve 40.

The relay unit E includes first pressure detection means 25, second pressure detection means 26, and third pressure detection means 56.

The first pressure detection means 25 is arranged between the first branch unit 10 and the second flow control device 13 on the second connection pipe 7.

The second pressure detection means 26 is arranged between the second flow control device 13 and the first flow control device 9.

The third pressure detection means 56 is arranged at a position where the first connection pipe 6 and the first bypass pipe 14 are connected.

The indoor unit includes first temperature detection means 53 and second temperature detection means 54.

The first temperature detection means 53 is arranged in the indoor unit on the first branch unit 10 side.

The second temperature detection unit 54 is arranged in the indoor unit on the second branch unit 11 side.

In other words, the first temperature detection means 53 and the second temperature detection means 54 are arranged at both ends of the indoor-side heat exchanger 5. The second temperature detection means 54 is connected on the first flow control device 9 side, whereas the first temperature detection means 53 is connected to the other end.

In addition, the heat-source-unit-side heat exchanger 3 includes a first heat-source-unit-side heat exchanger 41, a second heat-source-unit-side heat exchanger 42, a heat-source-unit-side bypass passage 43, a first solenoid opening/closing valve 44, a second solenoid opening/closing valve 45, a third solenoid opening/closing valve 46, a fourth solenoid opening/closing valve 47, and a fifth solenoid opening/closing valve 48. Note that, the heat-source-unit-side heat exchanger 3 includes the heat-source-unit-side fan 20 that controls heat exchange capacity of the heat-source-unit-side heat exchanger 3.

The first heat-source-unit-side heat exchanger 41 and the second heat-source-unit-side heat exchanger 42 have the same heat transfer area and are connected in parallel to each other.

The heat-source-unit-side bypass passage 43 is connected in parallel to the first heat-source-unit-side heat exchanger 41 and the second heat-source-unit-side heat exchanger 42.

The first solenoid opening/closing valve 44 is arranged at one end of the first heat-source-unit-side heat exchanger 41 on a side connected to the four-way switching valve 2.

The second solenoid opening/closing valve 45 is arranged at the other end of the first heat-source-unit-side heat exchanger 41.

The third solenoid opening/closing valve 46 is arranged at one end of the second heat-source-unit-side heat exchanger 42 on a side connected to the four-way switching valve 2.

The fourth solenoid opening/closing valve 47 is arranged at the other end of the second heat-source-unit-side heat exchanger 42.

The fifth solenoid opening/closing valve 48 is arranged in the middle of the heat-source-unit-side bypass passage 43.

In addition, the heat source unit A includes fourth pressure detection means 18. The fourth pressure detection means 18 is arranged in the middle of a pipe that connects the four-way switching valve 2 and a discharge portion of the compressor 1.

The air-conditioning apparatus 100 includes a controller 70. This controller 70 integrally controls the entire system of the air-conditioning apparatus 100. Specifically, the controller 70 controls a driving frequency of the compressor 1, a rotation speed of each of the heat-source-unit-side fan 20 and a fan arranged in the indoor-side heat exchanger 5, switching of the four-way switching valve 2, opening and closing of each solenoid valve, an opening degree of each expansion device, and the like. In other words, based on information detected by the temperature detection means and the pressure detection means as described above and an instruction from a remote controller (not shown), the controller 70 controls respective actuators (driving components for the compressor 1, the four-way switching valve 2, each solenoid valve (first solenoid opening/closing valve 44 to fifth solenoid opening/closing valve 48, and solenoid valve 31), each expansion device (first flow control device 9, second flow control device 13, third flow control device 15, and fourth flow control device 55) and the like).

Note that, a type of the refrigerant to be filled in the air-conditioning apparatus 100 is not particularly limited, and, for example, there may be used any of a natural refrigerant such as carbon dioxide (CO₂), a hydrocarbon, and helium, an alternative refrigerant that does not contain chlorine, such as HFC410A, HFC407C (zeotropic refrigerant mixture in which HFC-R32/R125/R134a are mixed at a ratio of 23/25/52 wt %), and HFC404A, and a fluorocarbon refrigerant such as R22 and R134a used for existing products.

An example case where the heat-source-unit-side heat exchanger 3 and the indoor-side heat exchanger 5 exchange heat between refrigerant and air has been described, but the heat may also be exchanged between refrigerant and a heat medium other than air, for example, water and brine.

In addition, this embodiment describes an example case where the air-conditioning apparatus 100 includes one heat source unit A, but the present invention is not limited thereto. The air-conditioning apparatus 100 may include two or more heat source units A. Further, an example case where the air-conditioning apparatus 100 includes three indoor units is described, but the present invention is not limited thereto. The air-conditioning apparatus 100 may include four or more indoor units. The controller 70 may be installed in any one of the heat source unit A, the indoor unit, and the relay unit E, and may also be installed in all of the heat source unit A, the indoor unit, and the relay unit E. In addition, the controller 70 may also be installed separately from the heat source unit A, the indoor unit, and the relay unit E. In addition, in the case of constructing the controller 70 with a plurality of components, the components are preferable to be communicably connected to each other by wired or wireless connection.

Next, an operation of the air-conditioning apparatus 100 is described.

[Cooling Operation]

First, an operation state for the cooling only operation is described referring to FIG. 2. FIG. 2 illustrates an example state where the cooling operation is performed by all of the indoor units B, C, and D.

As illustrated in FIG. 2, high-temperature and high-pressure refrigerant gas discharged from the compressor 1 passes through the four-way switching valve 2, and, in the heat-source-unit-side heat exchanger 3, exchanges heat with air that is sent by the heat-source-unit-side fan 20 that can change air-sending amount, to thereby condense and liquefy. Subsequently, the refrigerant passes sequentially through the third check valve 32, the second connection pipe 7, the gas-liquid separating device 12, and the second flow control device 13, and further through the second branch unit 11 and the second connection pipes 7 b, 7 c, and 7 d on the indoor unit side to flow into the respective indoor units B, C, and D.

Then, the refrigerant that flows into each of the indoor units B, C, and D is decompressed to low pressure by the first flow control device 9 that is controlled in accordance with the outlet superheating amount of each indoor-side heat exchanger 5. The decompressed refrigerant flows into the indoor-side heat exchanger 5, and exchanges heat with indoor air to evaporate and gasify, thereby cooling the indoor space. Then, the refrigerant in this gas state is sucked by the compressor 1 after passing through the first connection pipes 6 b, 6 c, and 6 d on the indoor unit side, the fourth flow control devices 55 in the first branch unit 10, the first connection pipe 6, the fourth check valve 33, the four-way switching valve 2, and the accumulator 4 in the heat source unit. In this way, the circulation cycle is constructed to perform the cooling operation.

At this time, each solenoid valve 31 is controlled to be closed. Further, because the first connection pipe 6 is at low pressure and the second connection pipe 7 is at high pressure, the refrigerant naturally flows into the third check valve 32 and the fourth check valve 33.

In addition, the opening degree of the fourth flow control device 55 is controlled based on the state of the refrigerant, which is obtained by the detection information from the third pressure detection means 56.

In addition, in this circulation cycle, a part of the refrigerant after passing through the second flow control device 13 enters the first bypass pipe 14. Then, after decompressed to low pressure by the third flow control device 15, the refrigerant exchanges heat in the second heat exchange unit 16 with refrigerant passing through the second flow control device 13 (refrigerant before branching off to flow into the first bypass pipe 14), to thereby evaporate. Further, in the first heat exchange unit 19, the refrigerant exchanges heat with refrigerant before flowing into the second flow control device 13, to thereby evaporate. This evaporated refrigerant enters the first connection pipe 6 and the fourth check valve 33, and passes through the four-way switching valve 2 and the accumulator 4 in the heat source unit to be sucked by the compressor 1.

On the other hand, the sufficiently-subcooled refrigerant, which is cooled by exchanging heat in the first heat exchange unit 19 and the second heat exchange unit 16 with the refrigerant that enters the first bypass pipe 14 and is decompressed to low pressure by the third flow control device 15, passes through the first check valves 50 b, 50 c, and 50 d in the second branch unit 11 and flows into the indoor units B, C, and D intended for cooling. Here, the capacity of the compressor 1 and the air-sending amount of the heat-source-unit-side fan 20, which are variable, are adjusted so that the evaporating temperature of the indoor unit and the condensing temperature of the heat-source-unit-side heat exchanger 3 reach predetermined target temperatures, thereby being capable of obtaining target cooling capacity in each indoor unit. Note that, the condensing temperature of the heat-source-unit-side heat exchanger 3 can be obtained as saturation temperature for the pressure detected by the fourth pressure detection means 18.

[Heating Operation]

Next, an operation state for the heating only operation is described referring to FIG. 3. FIG. 3 illustrates an example state where the heating operation is performed by all of the indoor units B, C, and D.

As illustrated in FIG. 3, the high-temperature and high-pressure refrigerant gas discharged from the compressor 1 passes sequentially through the four-way switching valve 2, the fifth check valve 34, the second connection pipe 7, the gas-liquid separating device 12, the solenoid valves 31 in the first branch unit 10, and the first connection pipes 6 b, 6 c, and 6 d on the indoor unit side, and flows into the indoor units B, C, and D. The refrigerant that flows into each of the indoor units B, C, and D exchanges heat with indoor air to condense and liquefy, thereby heating the indoor space. Then, the refrigerant in this state is controlled in accordance with the outlet subcooling amount of each indoor-side heat exchanger 5, and passes through the first flow control device 9.

The refrigerant after passing through the first flow control devices 9 flows from the second connection pipes 7 b, 7 c, and 7 d on the indoor unit side into the second branch unit 11, and joins together after passing through the second check valves 52 b, 52 c, and 52 d. The refrigerant that joins together in the second branch unit 11 is introduced further into the middle of the second connection pipe 7 between the second flow control device 13 and the second heat exchange unit 16, and passes through the third flow control device 15. In addition, here, the refrigerant is decompressed to low-pressure two-phase gas-liquid by the first flow control device 9 or the third flow control device 15.

Then, the refrigerant decompressed to low pressure passes through the first connection pipe 6 into the sixth check valve 35 and the heat-source-unit-side heat exchanger 3 in the heat source unit A, and exchanges heat in the heat source unit A with air sent by the heat-source-unit-side fan 20 that can change air-sending amount, to thereby evaporate. The refrigerant in the gas state resulting from the evaporation is sucked by the compressor 1 after passing through the four-way switching valve 2 and the accumulator 4. In this way, the circulation cycle is constructed to perform the heating operation.

At this time, each solenoid valve 31 is controlled to be opened.

In addition, the fourth flow control device 55 is closed.

In addition, because the first connection pipe 6 is at low pressure and the second connection pipe 7 is at high pressure in the circulation cycle, the refrigerant naturally flows into the fifth check valve 34 and the sixth check valve 35. In addition, because the pressure in the second connection pipes 7 b, 7 c, and 7 d on the indoor unit side is higher than the pressure in the second connection pipe 7, the first check valves 50 b, 50 c, and 50 d are closed. Here, the capacity of the compressor 1 and the air-sending amount of the heat-source-unit-side fan 20, which are variable, are adjusted so that the condensing temperature of the indoor unit and the evaporating temperature of the heat-source-unit-side heat exchanger 3 reach predetermined target temperatures, thereby being capable of obtaining target heating capacity in each indoor unit.

[Cooling Main Operation]

Next, an operation state for the cooling main operation is described referring to FIG. 4. FIG. 4 illustrates an example of the cooling main operation in a case where there are a cooling request from each of the indoor units B and C and a heating request from the indoor unit D.

As illustrated in FIG. 4, the high-temperature and high-pressure refrigerant gas discharged from the compressor 1 flows into the heat-source-unit-side heat exchanger 3 through the four-way switching valve 2, and exchanges heat in the heat-source-unit-side heat exchanger 3 with air sent by the heat-source-unit-side fan 20 that can change air-sending amount, thereby being brought into a two-phase high-temperature and high-pressure state.

Here, the capacity of the compressor 1 and the air-sending amount of the heat-source-unit-side fan 20, which are variable, are adjusted so that the evaporating temperature and the condensing temperature of the indoor unit reach predetermined target temperatures. In addition, the heat transfer area is adjusted by opening and closing the first solenoid opening/closing valve 44, the second solenoid opening/closing valve 45, the third solenoid opening/closing valve 46, and the fourth solenoid opening/closing valve 47 at both ends of the first heat-source-unit-side heat exchanger 41 and the second heat-source-unit-side heat exchanger 42. In addition, by opening and closing the fifth solenoid opening/closing valve 48 in the heat-source-unit-side bypass passage 43, a flow rate of the refrigerant that flows in the first heat-source-unit-side heat exchanger 41 and the second heat-source-unit-side heat exchanger 42 is adjusted. In this way, it is possible to obtain an arbitrary heat exchange amount in the heat-source-unit-side heat exchanger 3, and to obtain target heating capacity or cooling capacity in each indoor unit.

Subsequently, the refrigerant in the two-phase high-temperature and high-pressure state is sent to the gas-liquid separating device 12 in the relay unit E through the third check valve 32 and the second connection pipe 7, and is separated into gas-state refrigerant and liquid-state refrigerant.

Then, the gas-state refrigerant separated by the gas-liquid separating device 12 passes sequentially through the solenoid valve 31 in the first branch unit 10 and the first connection pipe 6 d on the indoor unit side, and flows into the indoor unit D that is intended for heating. Then, the gas-state refrigerant exchanges heat with indoor air by the indoor-side heat exchanger 5 to condense and liquefy, thereby heating the indoor space. Further, the refrigerant, which flows out of the indoor-side heat exchanger 5, passes through the first flow control device 9 that is controlled in accordance with the outlet subcooling amount of the indoor-side heat exchanger 5 in the indoor unit D to be decompressed to a small extent, and flows into the second branch unit 11. The refrigerant passes through the second bypass pipe 51 including the second check valve 52 d, and flows into a downstream part of the second flow control device 13 on the second connection pipe 7.

On the other hand, the liquid-state refrigerant separated by the gas-liquid separating device 12 passes through the second flow control device 13 that is controlled in accordance with the pressure detected by the first pressure detection means 25 and the pressure detected by the second pressure detection means 26, and joins the refrigerant passing through the indoor unit D intended for heating. Subsequently, the refrigerant flows into the second heat exchange unit 16 to be cooled by the second heat exchange unit 16.

Then, a part of the refrigerant cooled by the second heat exchange unit 16 passes through the first check valves 50 b and 50 c and the second connection pipes 7 b and 7 c on the indoor unit side, and flows into the indoor units B and C intended for cooling. The refrigerant that flows into each of the indoor units B and C enters the first flow control device 9 that is controlled in accordance with the outlet superheating amount of the indoor-side heat exchanger 5 in each of the indoor units B and C to be decompressed, and then enters the indoor-side heat exchanger 5 and exchanges heat to evaporate into a gas state, thereby cooling the indoor space. Subsequently, the refrigerant flows into the first connection pipe 6 through the fourth flow control device 55.

On the other hand, the rest of the refrigerant cooled by the second heat exchange unit 16 passes through the third flow control device 15 that is controlled so that a pressure difference between the pressure detected by the first pressure detection means 25 and the pressure detected by the second pressure detection means 26 falls within a predetermined range. Subsequently, after exchanging heat and evaporating in the second heat exchange unit 16 and the first heat exchange unit 19, the refrigerant flows into the thick first connection pipe 6 and joins the refrigerant passing through the indoor units B and C. The refrigerant that joins together in the first connection pipe 6 is sucked by the compressor 1 after passing through the fourth check valve 33, the four-way switching valve 2, and the accumulator 4 in the heat source unit A. In this way, the circulation cycle is constructed to perform the cooling main operation.

At this time, the solenoid valves 31 connected to the indoor units B and C are controlled to be closed, and the solenoid valve 31 connected to the indoor unit D is controlled to be opened.

In addition, the fourth flow control devices 55 connected to the indoor units B and C are opened, and the fourth flow control device 55 connected to the indoor unit D is closed.

In addition, because the first connection pipe 6 is at low pressure and the second connection pipe 7 is at high pressure, the refrigerant naturally flows into the third check valve 32 and the fourth check valve 33.

Further, because the pressure in each of the second connection pipes 7 b and 7 c on the indoor unit side is lower than the pressure in the second connection pipe 7, the second check valves 52 b and 52 c are closed.

In addition, because the pressure in the second connection pipe 7 d on the indoor unit side is higher than the pressure in the second connection pipe 7, the first check valve 50 d is closed.

The first check valves 50 and the second check valves 52 prevent the refrigerant, which passes through the indoor unit D with a request for heating, from flowing into the indoor units B and C with a request for cooling under a state in which the refrigerant fails to be sufficiently subcooled without passing through the second heat exchange unit 16.

[Heating Main Operation]

Next, an operation state for the heating main operation is described referring to FIG. 5. FIG. 5 illustrates an example of the heating main operation in a case where there are a heating request from each of the indoor units B and C and a cooling request from the indoor unit D.

As illustrated in FIG. 5, the high-temperature and high-pressure refrigerant gas discharged from the compressor 1 is sent to the relay unit E through the four-way switching valve 2, the fifth check valve 34, and the second connection pipe 7, and passes through the gas-liquid separating device 12. The refrigerant passing through the gas-liquid separating device 12 passes sequentially through the solenoid valves 31 in the first branch unit 10 and the first connection pipes 6 b and 6 c on the indoor unit side, and flows into the indoor units B and C intended for heating. Then, the refrigerant exchanges heat with indoor air in each indoor-side heat exchanger 5 to condense and liquefy, thereby heating the indoor space. The refrigerant condensed and liquefied is controlled in accordance with the outlet subcooling amount of the indoor-side heat exchanger 5 in each of the indoor units B and C, and passes through the first flow control device 9 to be decompressed to a small extent. Then, the refrigerant flows into the second branch unit 11.

The refrigerant that flows into the second branch unit 11 passes through the second bypass pipe 51 including the second check valves 52 b and 52 c, and joins the refrigerant in the second connection pipe 7 to be cooled in the second heat exchange unit 16. A part of the refrigerant cooled by the second heat exchange unit 16 passes through the first check valve 50 d and the second connection pipe 7 d on the indoor unit side, and enters the indoor unit D intended for cooling. Then, the refrigerant after entering the indoor unit D enters the first flow control device 9 that is controlled in accordance with the outlet superheating amount of the indoor-side heat exchanger 5 to be decompressed, and subsequently enters the indoor-side heat exchanger 5 and exchanges heat to evaporate into a gas state, thereby cooling the indoor space. Then, the refrigerant flows into the first connection pipe 6 through the fourth flow control device 55.

On the other hand, the rest of the refrigerant cooled by the second heat exchange unit 16 passes through the third flow control device 15 that is controlled so that the pressure difference between the pressure detected by the first pressure detection means 25 and the pressure detected by the second pressure detection means 26 falls within the predetermined range. The refrigerant after passing through the third flow control device 15 exchanges heat in the second heat exchange unit 16 with refrigerant flowing out of the heating indoor units, to thereby evaporate. Subsequently, the refrigerant joins the refrigerant passing through the indoor unit D intended for cooling, and flows into the sixth check valve 35 and the heat-source-unit-side heat exchanger 3 in the heat source unit A through the thick first connection pipe 6. The refrigerant that flows into the heat-source-unit-side heat exchanger 3 exchanges heat with air that is sent by the heat-source-unit-side fan 20 that can change air-sending amount, to thereby evaporate into a gas state.

Here, the capacity of the compressor 1 and the air-sending amount of the heat-source-unit-side fan 20, which are variable, are adjusted so that the evaporating temperature of the indoor unit D with a request for cooling and the condensing temperature of each of the indoor units B and C with a request for heating fall within predetermined target temperatures. In addition, the heat transfer area is adjusted by opening and closing the first solenoid opening/closing valve 44, the second solenoid opening/closing valve 45, the third solenoid opening/closing valve 46, and the fourth solenoid opening/closing valve 47 at both ends of the first heat-source-unit-side heat exchanger 41 and the second heat-source-unit-side heat exchanger 42. In addition, by opening and closing the fifth solenoid opening/closing valve 48 in the heat-source-unit-side bypass passage 43, the flow rate of the refrigerant that flows in the first heat-source-unit-side heat exchanger 41 and the second heat-source-unit-side heat exchanger 42 is adjusted. In this way, it is possible to obtain an arbitrary heat exchange amount in the heat-source-unit-side heat exchanger 3, and to obtain target heating capacity or cooling capacity in each indoor unit. Then, the refrigerant is sucked by the compressor 1 after passing through the four-way switching valve 2 and the accumulator 4 in the heat source unit A. In this way, the circulation cycle is constructed to perform the heating main operation.

At this time, the solenoid valves 31 connected to the indoor units B and C are controlled to be opened, and the solenoid valve 31 connected to the indoor unit D is controlled to be closed. In addition, the fourth flow control devices 55 connected to the indoor units B and C are closed, and the fourth flow control device 55 connected to the indoor unit D is opened.

In addition, because the first connection pipe 6 is at low pressure and the second connection pipe 7 is at high pressure, the refrigerant naturally flows into the fifth check valve 34 and the sixth check valve 35. At this time, the second flow control device 13 is closed.

Further, because the pressure in each of the second connection pipes 7 b and 7 c on the indoor unit side is higher than the pressure in the second connection pipe 7, the first check valves 50 b and 50 c are closed.

In addition, because the pressure in the second connection pipe 7 d on the indoor unit side is lower than the pressure in the second connection pipe 7, the second check valve 52 d is closed.

The first check valves 50 and the second check valves 52 prevent the refrigerant, which pass through each of the heating indoor units B and C, from flowing into the cooling indoor unit D under a state in which the refrigerant fails to be sufficiently subcooled without passing through the second heat exchange unit 16.

[Control of Opening Degree of Fourth Flow Control Device 55]

The opening degree of the fourth flow control device 55 is controlled based on the state of the refrigerant, which is obtained based on detection information from the third pressure detection means 56. In other words, the controller 70 determines the state of the refrigerant that flows into the fourth flow control device 55 based on pressure information detected by the third pressure detection means 56 to appropriately maintain the opening degree of the fourth flow control device 55 based on a result of the determination.

Note that, the example above describes the case where the state of the refrigerant that flows into the fourth flow control device 55 is determined based on the detection information from the third pressure detection means 56, but the present invention is not limited thereto. Information from other detection means may also be used as described below.

For example, the state of the refrigerant that flows into the fourth flow control device 55 may also be determined by estimating a pressure difference value at an inlet and outlet of the fourth flow control device 55 based on the information from the third pressure detection means 56 and the first temperature detection means 53 (see FIG. 8).

In addition, the state of the refrigerant that flows into the fourth flow control device 55 may also be determined based on the outlet subcooling value of the indoor-side heat exchanger 5 that performs the heating operation before switching to the cooling operation (see FIG. 9).

Further, the state of the refrigerant that flows into the fourth flow control device 55 may also be determined by estimating the state of the refrigerant in the idle indoor unit based on an elapsed time period since the stop of heating (see FIG. 10).

Still further, the state of the refrigerant that flows into the fourth flow control device 55 may also be determined by combining those methods.

FIG. 7 is a flowchart illustrating an example flow of processing for controlling the opening degree of the fourth flow control device 55 during a refrigerant noise suppression operation. FIGS. 8 to 10 are flowcharts each illustrating an example flow of processing for determining whether or not the refrigerant noise suppression operation is necessary. Referring to FIGS. 7 to 10, the refrigerant noise suppression operation in the fourth flow control device 55 is described. Note that, the controller 70 is a main controller in FIGS. 7 to 10.

First, referring to FIG. 7, the flow of the processing during the refrigerant noise suppression operation is described.

When the refrigerant noise suppression operation is started (Step S101), the controller 70 controls the opening degree of the fourth flow control device 55 to be slightly opened (Step S102). Then, the controller 70 determines whether or not the refrigerant noise suppression operation is necessary (Step S103). Whether or not the refrigerant noise suppression operation is necessary is determined in accordance with the flowcharts of FIGS. 8 to 10 described later.

When it is determined that the refrigerant noise suppression operation is necessary (Step S103; YES), the controller 70 increases the opening degree of the fourth flow control device 55 (Step S104). Next, the controller 70 determines whether or not the opening degree of the fourth flow control device 55 is at a maximum (Max opening degree) (Step S105). On the other hand, when it is determined that the refrigerant noise suppression operation is not necessary (Step S103; NO), the controller 70 finishes the refrigerant noise suppression operation (Step S106).

When it is determined that the opening degree of the fourth flow control device 55 is at a maximum (Step S105; YES), the controller 70 finishes the refrigerant noise suppression operation (Step S106). On the other hand, when it is determined that the opening degree of the fourth flow control device 55 is not at a maximum (Step S105; NO), the controller 70 reconfirms whether or not the refrigerant noise suppression operation is necessary (Step S103).

Next, referring to FIG. 8, an example flow of processing for determining whether or not the refrigerant noise suppression operation is necessary is described. In FIG. 8, whether or not the refrigerant noise suppression operation is necessary is determined based on a front and back pressure difference of the fourth flow control device 55.

When determining (reconfirming) whether or not the refrigerant noise suppression operation is necessary (Step S103 in FIG. 7 and Step S101 a), the controller 70 determines whether or not a front and back pressure difference ΔPa of the fourth flow control device 55 is equal to or greater than a predetermined target pressure difference ΔP0 (Step S102 a). Then, when ΔPa is equal to or greater than ΔP0 (Step S102 a; YES), the controller 70 determines that the refrigerant noise suppression operation is necessary (Step S104 a). On the other hand, when ΔPa is smaller than ΔP0 (Step S102 a; NO), the controller 70 finishes the refrigerant noise suppression operation and returns to a regular operation (Step S103 a).

Note that, for pressure on a low pressure side of the fourth flow control device 55, the third pressure detection means 56 only needs to be used. In addition, for pressure on a high pressure side of the fourth flow control device 55, the saturation temperature on the indoor unit side may be estimated by using the first temperature detection means 53.

Next, referring to FIG. 9, an example flow of processing for determining whether or not the refrigerant noise suppression operation is necessary is described. In FIG. 9, whether or not the refrigerant noise suppression operation is necessary is determined based on subcooling in the indoor unit during the heating operation.

When determining (reconfirming) whether or not the refrigerant noise suppression operation is necessary (Step S103 in FIG. 7 and Step S101 b), the controller 70 determines whether or not subcooling SCa in the indoor unit during the heating operation is equal to or greater than predetermined target subcooling SC0 (Step S102 b). Then, when SCa is equal to or greater than SC0 (Step S102 b; YES), the controller 70 determines that the refrigerant noise suppression operation is necessary (Step S104 b). On the other hand, when SCa is smaller than SC0 (Step S102 b; NO), the controller 70 finishes the refrigerant noise suppression operation and returns to the regular operation (Step S103 b).

Note that, the saturation temperature of the indoor unit during the heating operation may be estimated by using the first pressure detection means 25. In addition, a subcooling value (SC value) may be calculated based on the saturation temperature estimated by using the second temperature detection means 54 and the first pressure detection means 25.

Next, referring to FIG. 10, an example flow of processing for determining whether or not the refrigerant noise suppression operation is necessary is described. In FIG. 10, whether or not the refrigerant noise suppression operation is necessary is determined based on the elapsed time period since the end of the heating operation.

When determining (reconfirming) whether or not the refrigerant noise suppression operation is necessary (Step S103 in FIG. 7 and Step S101 c), the controller 70 determines whether or not an elapsed time period Ta since the end of the heating operation is equal to or greater than a predetermined target elapsed time period TO (Step S102 c). Then, when Ta is equal to or greater than TO (Step S102 c; YES), the controller 70 determines that the refrigerant noise suppression operation is necessary (Step S104 c). On the other hand, when Ta is smaller than TO (Step S102 c; NO), the controller 70 finishes the refrigerant noise suppression operation and returns to the regular operation (Step S103 c).

Whether or not the refrigerant noise suppression operation is necessary is described above separately referring to the flowcharts of FIGS. 8 to 10, but whether or not the refrigerant noise suppression operation is necessary may also be determined by combining those methods as appropriate.

As described above, according to the air-conditioning apparatus 100, the opening degree of the fourth flow control device 55 can be maintained in an appropriate state, thereby being capable of significantly reducing the refrigerant flow noise that may be generated when the heating operation is switched to the cooling operation as compared to the configuration in which the first branch unit includes a plurality of solenoid valves. In addition, according to the air-conditioning apparatus 100, it is not necessary to equalize the refrigerant pressure regardless of the amount of the high-temperature and high-pressure liquid refrigerant flowing from the first connection pipe 6 on the indoor unit side, thereby being capable of reducing the startup time period of the indoor unit. Thus, according to the air-conditioning apparatus 100, it is possible to significantly enhance comfort.

REFERENCE SIGNS LIST

-   -   1 compressor     -   2 four-way switching valve     -   3 heat-source-unit-side heat exchanger     -   4 accumulator     -   5 indoor-side heat exchanger     -   6 first connection pipe     -   6 b first connection pipe     -   6 d first connection pipe     -   7 second connection pipe     -   7 b second connection pipe     -   7 d second connection pipe     -   9 first flow control device     -   10 first branch unit     -   11 second branch unit     -   12 gas-liquid separating device     -   13 second flow control device     -   14 first bypass pipe     -   15 third flow control device     -   16 second heat exchange unit     -   18 fourth pressure detection means     -   19 first heat exchange unit     -   20 heat-source-unit-side fan     -   25 first pressure detection means     -   26 second pressure detection means     -   31 solenoid valve     -   32 third check valve     -   33 fourth check valve     -   34 fifth check valve     -   35 sixth check valve     -   40 heat-source-unit-side switching valve     -   41 first heat-source-unit-side heat exchanger     -   42 second heat-source-unit-side heat exchanger     -   43 heat-source-unit-side bypass passage     -   44 first solenoid opening/closing valve     -   45 second solenoid opening/closing valve     -   46 third solenoid opening/closing valve     -   47 fourth solenoid opening/closing valve     -   48 fifth solenoid opening/closing valve     -   50 first check valve     -   50 b first check valve     -   50 c first check valve     -   50 d first check valve     -   51 second bypass pipe     -   52 second check valve     -   52 b second check valve     -   52 d second check valve     -   53 first temperature detection means     -   54 second temperature detection means     -   55 fourth flow control device     -   56 third pressure detection means     -   70 control device     -   100 air-conditioning apparatus     -   A heat source unit     -   B indoor unit     -   C indoor unit     -   D indoor unit     -   E relay unit 

1. An air-conditioning apparatus, which is configured by connecting a heat source unit and a plurality of indoor units through a first connection pipe and a second connection pipe to supply refrigerant from the heat source unit to each of the plurality of indoor units to perform a cooling operation and/or a heating operation, the heat source unit including a compressor, a switching valve, and a heat-source-unit-side heat exchanger, each of the plurality of indoor units including an indoor-side heat exchanger and a first flow control device, the air-conditioning apparatus including: a first branch unit for switchably connecting one of a refrigerant inlet and a refrigerant outlet of the indoor-side heat exchanger of each of the plurality of indoor units to the first connection pipe or the second connection pipe; and a second branch unit connected on one side thereof to the second connection pipe and split on an other side thereof into a plurality of branches each connected to an other one of the refrigerant inlet and the refrigerant outlet of the indoor-side heat exchanger of each of the plurality of indoor units through the first flow control device, the first branch unit including: a branch-side flow control device provided to each of a plurality of pipes split from the first connection pipe and connected to the indoor-side heat exchanger of corresponding one of the plurality of indoor units; and a solenoid valve provided to each of pipes split from a pipe connecting the branch-side flow control device and the indoor-side heat exchanger of corresponding one of the plurality of indoor units, wherein an opening degree of the branch-side flow control device is controlled based on a state of the refrigerant to be caused to flow into the branch-side flow control device, wherein the state of the refrigerant to be caused to flow into the branch-side flow control device is determined based on an outlet subcooling value of the indoor-side heat exchanger that performs the heating operation before switching to the cooling operation. 2-8. (canceled)
 9. An air-conditioning apparatus, which is configured by connecting a heat source unit and a plurality of indoor units through a first connection pipe and a second connection pipe to supply refrigerant from the heat source unit to each of the plurality of indoor units to perform a cooling operation and/or a heating operation, the heat source unit including a compressor, a switching valve, and a heat-source-unit-side heat exchanger, each of the plurality of indoor units including an indoor-side heat exchanger and a first flow control device, the air-conditioning apparatus including: a first branch unit for switchably connecting one of a refrigerant inlet and a refrigerant outlet of the indoor-side heat exchanger of each of the plurality of indoor units to the first connection pipe or the second connection pipe; and a second branch unit connected on one side thereof to the second connection pipe and split on an other side thereof into a plurality of branches each connected to an other one of the refrigerant inlet and the refrigerant outlet of the indoor-side heat exchanger of each of the plurality of indoor units through the first flow control device, the first branch unit including: a branch-side flow control device provided to each of a plurality of pipes split from the first connection pipe and connected to the indoor-side heat exchanger of corresponding one of the plurality of indoor units; and a solenoid valve provided to each of pipes split from a pipe connecting the branch-side flow control device and the indoor-side heat exchanger of corresponding one of the plurality of indoor units, wherein an opening degree of the branch-side flow control device is controlled based on a state of the refrigerant to be caused to flow into the branch-side flow control device, wherein the state of the refrigerant to be caused to flow into the branch-side flow control device is determined by estimating an inlet-outlet pressure difference of the branch-side flow control device. 